Environmental influences on mare reproductive loss syndrome: Do they fit with a toxin as the causative agent?

Mare Reproductive Loss Syndrome (MRLS) is the term given to abortions in mares associated with Eastern Tent caterpillars (ETC; Malacosoma americanum). This paper aims to examine if the hypothesis for a toxin as the cause of MRLS holds up to testing using Westerman's Correlates of Causal Strength of Evidence (WCCSE) and fits with known environmental factors that influence the occurrence of MRLS. Using WCCSE all correlates fit with a toxin as a potential causative agent. Environmental factors also fitted with this hypothesis. MRLS events were associated with higher than normal ambient temperatures and lower than normal precipitation. Higher temperatures facilitated a rapid tightly grouped hatching interval which produced a higher population density of ETCs during a specific time period and encouraged more active ingestion of Black Cherry tree leaves. These leaves contain prunasin, the precursor of a toxin produced by the ETCs, which protects the caterpillars from predation. ETCs serve as the vector for the toxin which contaminated pasture and water during off-tree feeding bouts. The toxin accumulated on the pasture forage in the absence of rainfall, thus increasing exposure and clinical responses. Precipitation diluted the contaminate which reduced the toxin dose and clinical affects following ingestion of the contaminated grass or water. The pathogenesis of MRLS remains unconfirmed. However, the potential role of a toxin in this syndrome should be considered.